FR3131439A1 - Image sensor - Google Patents

Abstract

Image sensor The present description relates to an image sensor comprising a plurality of pixels (100) formed in and on a semiconductor substrate (101), each pixel comprising: – at least a first photosensitive zone (103) formed in the substrate semiconductor (101) and adapted to pick up light in a first range of wavelengths; - a second photosensitive zone (105) formed in the semiconductor substrate (101) directly above said at least one first photosensitive zone (103) and adapted to pick up light in a second range of wavelengths, different from the first wavelength range; - at least one charge collection area (113) disposed on the side (101T) of the substrate (101) opposite said at least one first photosensitive area (103); - at least one transfer region extending from said at least one first photosensitive area (103) to said at least one charge collection area (113); and - at least one transfer gate (TG) extending vertically between said at least one transfer region and the second photosensitive area and laterally bordering said at least one transfer region. Figure for abstract: Fig. 2

Description

Image sensor

The present description generally concerns the field of image acquisition devices. The present description relates more particularly to image acquisition devices adapted to acquire a 2D image and a depth image of a scene.

Image acquisition devices capable of acquiring a 2D image and a depth image of a scene are known. In particular, devices are known comprising 2D image sub-pixels and depth sub-pixels integrated into an array of pixels of the same image sensor.

There is a need to improve existing devices for acquiring a 2D image and a depth image of a scene. It would be desirable to produce an image sensor integrating, in the same network of pixels, 2D image sub-pixels and depth sub-pixels, the sensor presenting in particular, for the acquisition of depth images, a efficiency superior to that of known sensors.

An object of one embodiment is to overcome all or part of the drawbacks of known devices for acquiring a 2D image and a depth image of a scene.

For this, one embodiment provides an image sensor comprising a plurality of pixels formed in and on a semiconductor substrate, each pixel comprising:
– at least a first photosensitive zone formed in the semiconductor substrate and adapted to capture light in a first range of wavelengths;
– a second photosensitive zone formed in the semiconductor substrate directly above said at least one first photosensitive zone and adapted to capture light in a second wavelength range, different from the first wavelength range;
– at least one charge collection zone arranged on the side of the substrate opposite to said at least one first photosensitive zone;
– at least one transfer region extending from said at least one first photosensitive zone to said at least one charge collection zone; And
– at least one transfer grid extending vertically between said at least one transfer region and the second photosensitive zone and laterally bordering said at least one transfer region.

According to one embodiment, each pixel further comprises a peripheral insulation trench extending vertically in the semiconductor substrate, from said side of the second photosensitive zone, and laterally delimiting said at least one first photosensitive zone and the second photosensitive zone .

According to one embodiment, each transfer gate comprises a first insulation trench extending into the semiconductor substrate from said side of the substrate opposite said at least one first photosensitive zone and partially penetrating into the thickness of said at least one first photosensitive area.

According to one embodiment, each charge collection zone extends laterally between the peripheral insulation trench and the or one of the first insulation trenches.

According to one embodiment, each transfer gate is surrounded by a second insulation trench extending vertically in the substrate from said side of the substrate opposite to said at least one first photosensitive zone.

According to one embodiment, each pixel further comprises at least one other transfer gate extending laterally on said side of the substrate opposite to said at least one first photosensitive zone and at least one other charge collection zone.

According to one embodiment, each pixel has four first photosensitive zones.

According to one embodiment, the first photosensitive zones are isolated from each other by a third isolation trench.

According to one embodiment, the second photosensitive zone is on and in contact with the first photosensitive zone.

According to one embodiment, the sensor further comprises a control circuit configured to apply alternately, to said at least one transfer grid:
– a first potential adapted to block a transfer of charges from said at least one first photosensitive zone to said at least one charge collection zone; And
– a second potential, different from the first potential, adapted to allow a transfer of charges from said at least one first photosensitive zone to said at least one charge collection zone.

According to one embodiment, the first photosensitive areas of the sensor pixels are intended to capture a 2D image and the second photosensitive areas of the sensor pixels are intended to capture a depth image.

These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments given on a non-limiting basis in relation to the attached figures, among which:

there is a schematic and partial top view of an image sensor pixel according to one embodiment;

there is a sectional view, according to plan AA of the , from the pixel of the ;

there is a sectional view, according to plan BB of the , from the pixel of the ;

there is a schematic and partial top view of an image sensor pixel according to another embodiment;

there is a sectional view, according to plan AA of the , from the pixel of the ;

there is a sectional view, according to plan AA of the , of a step of a process for manufacturing the pixel of the ;

there is a sectional view, according to plan AA of the , a step in the process of manufacturing the pixel of the ;

there is a sectional view, according to plan BB of the , a step in the process of manufacturing the pixel of the ;

there is a sectional view, according to plan AA of the , a step in the process of manufacturing the pixel of the ; And

there is a sectional view, according to plan BB of the , a step in the process of manufacturing the pixel of the .

The same elements have been designated by the same references in the different figures. In particular, the structural and/or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

For the sake of clarity, only the steps and elements useful for understanding the embodiments described have been represented and are detailed. In particular, the circuits (transistors and connections) of the pixels have not been detailed, the embodiments and variants described being compatible with the usual pixel circuits. Furthermore, the reading circuits, or column decoders, the control circuits, or line decoders, and the applications in which image sensors can be provided have not been detailed, the embodiments and variants described being compatible with the reading circuits and the control circuits of usual image sensors, as well as with the usual applications using image sensors.

Unless otherwise specified, when we refer to two elements connected to each other, this means directly connected without intermediate elements other than conductors, and when we refer to two elements connected (in English "coupled") to each other, this means that these two elements can be connected or be linked through one or more other elements.

We designate by “transmittance of a layer” the ratio between the intensity of the radiation leaving the layer and the intensity of the radiation entering the layer. In the remainder of the description, a layer or film is said to be opaque to radiation when the transmittance of the radiation through the layer or film is less than 10%. In the remainder of the description, a layer or film is said to be transparent to radiation when the transmittance of the radiation through the layer or film is greater than 10%.

In the remainder of the description, "visible light" designates electromagnetic radiation whose wavelength is between 380 nm and 780 nm and "infrared radiation" designates electromagnetic radiation whose wavelength is between 780 nm and 780 nm. 15 µm. In addition, “near infrared radiation” refers more particularly to electromagnetic radiation whose wavelength is between 780 nm and 1.7 µm.

In the following description, when referring to absolute position qualifiers, such as "front", "back", "up", "down", "left", "right", etc., or relative, such as the terms "above", "below", "superior", "lower", etc., or to qualifiers of orientation, such as the terms "horizontal", "vertical", etc., it is referred to unless otherwise specified in the orientation of the figures.

Unless otherwise specified, the expressions "approximately", "approximately", "substantially", and "of the order of" mean to the nearest 10%, preferably to the nearest 5%.

There is a schematic and partial top view of an image sensor pixel 100 according to one embodiment. Figures 2 and 3 are sectional views, according to plans AA and BB of the , respectively, of pixel 100 of the .

In the example shown, the pixel 100 is formed in and on a semiconductor substrate 101, for example made of silicon. For example, the substrate 101 has a thickness of between 5 and 20 μm.

In the example shown, the pixel 100 comprises first photosensitive zones 103 formed in the semiconductor substrate 101. As illustrated in , each photosensitive zone 103 extends vertically in the thickness of the semiconductor substrate 101 from a lower face 101B of the substrate 101 and to a depth less than the thickness of the substrate 101. In the example illustrated, the pixel 100 comprises more precisely four first photosensitive zones 103. Each photosensitive zone 103 has, seen from above, a circumference of approximately square shape. The four photosensitive zones 103 are, in the example shown, coplanar and arranged, in top view, in a generally substantially square shape. The photosensitive zones 103 are for example formed in a region of the substrate 101 doped with a first type of conductivity, for example the n type.

In the example shown, the pixel 100 further comprises a second photosensitive zone 105 formed in the semiconductor substrate 101. The second photosensitive zone 105 is located directly above the first photosensitive zones 103 (above the first photosensitive zones 103, in the orientation of Figures 2 and 3). As illustrated in Figures 2 and 3, the photosensitive zone 105 extends vertically in the thickness of the semiconductor substrate 101 from an upper face 101T of the substrate 101, opposite the lower face 101B. Seen from above, the photosensitive zone 105 has a substantially square perimeter. In this example, the photosensitive zone 105 has lateral dimensions substantially equal to those of the square formed by the four photosensitive zones 103. The photosensitive zone 105 is for example formed in a region of the substrate 101 doped with a second type of conductivity opposite to the first type of conductivity, type p in this example. For example, the substrate 101 has, in the region where the photosensitive zone 105 is formed, a doping rate of between 1 x 10 ¹⁰ and 1 x 10 ^{1 7} at./cm ³ . In this example, the second photosensitive zone 105 is in contact, via its lower face, with the upper face of the underlying first photosensitive zones 103.

Each photosensitive zone 103, 105 is for example intended to collect photons, during illumination phases of the image sensor of which pixel 100 is a part, and to convert these photons into electron-hole pairs. In this example, the first photosensitive zones 103 are adapted to capture light in a first range of wavelengths and the second photosensitive zone 105 is adapted to capture light in a second range of wavelengths, different from the first wavelength range. The first photosensitive zones 103 are for example intended to capture 2D images and the second photosensitive zone 105 is for example intended to capture depth images. For example, the photosensitive zones 103 of the pixel 100 are adapted to capture visible light, for example blue light, and the photosensitive zone 105 of the pixel 100 is adapted to capture infrared radiation, for example infrared radiation. close.

In the example shown where the first photosensitive zones and the second photosensitive zone are made of the same material, for example silicon, the visible light and the infrared radiation are mainly absorbed at different depths in the substrate 101 from its lower face 101B. In this example, the majority absorption depth of visible light is lower than that of infrared radiation. For example, the second photosensitive zone has a thickness greater than that of the first photosensitive zones, in order to optimize the absorption of infrared radiation in the second photosensitive zone. As a variant, it can be provided that the first photosensitive zones are made of a first material, for example silicon, and that the second photosensitive zone is made of a second material different from the first material, for example germanium or a silicon-germanium alloy. . The first and second materials are then respectively adapted to absorb mainly infrared and visible radiation.

In the example shown, the pixel 100 further comprises a peripheral insulation trench 107, for example a capacitive insulation trench, laterally delimiting the second photosensitive zone 105 and the arrangement formed by the first photosensitive zones 103. More precisely , in this example, the peripheral insulation trench 107 completely surrounds the photosensitive zone 105 and has, in top view, a contour of substantially square shape.

The peripheral isolation trench 107 makes it possible to electrically isolate the photosensitive zones 103 and 105 of the pixel 100 with respect to the photosensitive zones of neighboring pixels, not shown in Figures 1 to 3. The peripheral insulation trench 107 is formed in the substrate 101. In the orientation of Figures 2 and 3, the peripheral insulation trench 107 extends vertically in the thickness of the substrate 101 from the upper face 101T of the substrate 101 and to the lower face 101B of the substrate 101. In other words, the peripheral insulation trench 107 extends vertically, in this example, over the entire thickness of the substrate 101 and opens out on the side of the upper 101T and lower 101B faces of the substrate 101.

The peripheral isolation trench 107 has for example a width of between 200 and 600 nm, and a depth of between 1 and 20 µm. In the example illustrated in Figures 2 and 3, the peripheral insulation trench 107 has a depth equal to the thickness of the substrate 101.

Although this has not been detailed in Figures 1 to 3, the peripheral insulation trench 107 includes for example an electrically conductive region whose side walls are coated with an electrically insulating layer. The electrically insulating layer electrically insulates the electrically conductive region of the trench 107 relative to the substrate 101. For example, the electrically conductive region of the trench 107 is made of polycrystalline silicon, of a metal, for example copper, or of a metal alloy and the electrically insulating layer of the trench 107 is made of a dielectric material, for example silicon oxide. For example, the peripheral isolation trench 107 is a CDTI (Capacitive Deep Trench Isolation) type trench, or deep capacitive insulation trench.

In the example shown, the first photosensitive zones 103 of the pixel 100 are separated from each other by an insulation trench 109, for example a capacitive insulation trench, for example of the CDTI type. In this example, the pixel 100 comprises more precisely an insulation trench 109 having, in top view, a general cross shape substantially centered in relation to the pixel 100. As illustrated in Figures 2 and 3, the insulation trench 109 extends vertically in the thickness of the semiconductor substrate 101 from the lower face 101B of the substrate 101 to the photosensitive zone 105, without however opening onto the side of the upper face 101T of the substrate 101, the insulation trench 109 having by example, as illustrated in Figures 2 and 3, a height substantially equal to the thickness of the first photosensitive zones 103. In the example shown, each first photosensitive zone 103 is thus bordered laterally by the peripheral insulation trench 107 and by the insulation trench 109. For example, the trench 109 has a structure similar to that of the trench 107. More precisely, the trench 109 can for example present an electrically conductive region, for example a metallic region, or a region charged, for example charged polycrystalline silicon, the sides of which are coated with an electrically insulating layer. As a variant, the trench 109 is a charged insulation trench, for example of the DTI (Deep Trench Isolation) type, or deep charged insulation trench. In this case, the trench 109 is for example devoid of an electrically conductive region.

In the example illustrated in Figures 1 to 3, the pixel 100 further comprises four vertical transfer grids TG each comprising an insulation trench 111, for example a capacitive insulation trench. In this example, each insulation trench 111 has, in top view, a general L shape. As illustrated in Figures 2 and 3, each insulation trench 111 extends vertically in the thickness of the semiconductor substrate 101 from the upper face 101T of the substrate 101 up to one of the first photosensitive zones 103, and partially penetrates into the photosensitive zone 103 to a depth less than that of the peripheral insulation trench 107. In other words, each insulation trench 111 is interrupted in the thickness of the substrate 101 and does not open onto the side of the lower face 101B of the substrate 101. For example, each insulation trench 111 has a depth of between 3 and 18 µm.

In this example, the insulation trenches 111 are, in top view, located at the four corners of the square formed by the peripheral insulation trench 107. The insulation trenches 111 are more precisely arranged so as to delimit regions of the substrate 101 having, in top view, a substantially square shape. In the example illustrated in , parts of the substrate 101 are interposed between the ends of the L formed by each insulation trench 111 and the walls of the peripheral insulation trench 107 located opposite.

Each insulation trench 111 has for example a structure similar to that of the peripheral insulation trench 107. More precisely, although this has not been detailed in Figures 1 to 3, each insulation trench 111 comprises for example an electrically conductive region, for example made of polycrystalline silicon, a metal, for example copper, or a metal alloy. The electrically conductive region of each insulation trench 111 is for example made of the same material as the electrically conductive region of the peripheral insulation trench 107. In addition, each trench 111 comprises for example an electrically insulating layer covering the side walls and the underside of the electrically conductive region. The electrically insulating layer electrically insulates the electrically conductive region of the trench 111 relative to the substrate 101. For example, the electrically insulating layer of each trench 111 is made of a dielectric material, for example silicon oxide. The electrically insulating layer of each insulation trench 111 is for example made of the same material as the electrically insulating layer of the peripheral insulation trench 107.

The electrically conductive region of each insulation trench 111 is for example electrically isolated from the electrically conductive region of the peripheral insulation trench 107. This makes it possible, for example, to polarize the electrically conductive region of each insulation trench 111 independently of the electrically conductive region of the peripheral insulation trench 107.

In the example shown, the pixel 100 further comprises charge collection zones 113 arranged on the side of the substrate opposite the first photosensitive zones 103, that is to say on the side of the face 101T of the substrate. In the orientation of the , the charge collection zones 113 extend vertically in the thickness of the substrate 101 from its upper face 101T, to a depth less than that of the insulation trenches 111. In this example, each charge collection zone 113 is surrounded by one of the insulation trenches 111 and by the peripheral insulation trench 107. For example, each charge collection zone 113 has, seen from above, a substantially square shape. Each charge collection zone 113 is for example more heavily doped with the second type of conductivity, in this example the p type (p+), than the photosensitive zone 105. For example, the substrate 101 has, at the location where each charge collection zone 113 is formed, a doping rate of between 1 x 10 ¹⁶ and 5 x 10 ²⁰ at./cm ³ .

In the example shown, each first photosensitive zone 103 comprises a region 115 doped with the second type of conductivity, the p type in this example. Regions 115 are for example heavily doped with p-type (p+). In this example, the regions 115 extend vertically in the thickness of the substrate 101 from one face of the photosensitive zones 103 located on the side of the photosensitive zone 105 to a depth less than the thickness of the photosensitive zones 103. Inside each first photosensitive zone 103, the region 115 forms, with a part of the substrate 101 doped with the first type of conductivity, the n type in this example, a photodiode. Region 115 also makes it possible to block charge transfers from photosensitive zones 103 to photosensitive zone 105 of pixel 101. As a variant, region 115 can be omitted, for example in a case where the vertical transfer grid TG is close to isolation trench 109.

In the example shown, the photosensitive zone 105 includes a region 117 doped with the first type of conductivity, type n in this example. In this example, the region 117 extends vertically in the thickness of the substrate 101 from its upper face 101T to a depth less than the thickness of the second photosensitive zone 105. In the example illustrated in , the region 117 has a substantially square shape and is substantially centered with respect to the peripheral insulation trench 107 of the pixel 100. Inside the second photosensitive zone 105, the region 117 forms, with a part of the substrate 101 doped of the second type of conductivity, the p type in this example, a photodiode.

In the example shown, pixel 100 further comprises charge collection zones 119 arranged on the side of the substrate opposite to the first photosensitive zones 103, that is to say on the side of the upper face 101T of the substrate. In the orientation of the , the charge collection zones 119 extend vertically in the thickness of the substrate 101 from its upper face 101T to a depth less than the thickness of the region 117. In this example, the pixel 100 comprises more precisely three charge collection zones 119 each located between one of the sides of the region 117 and one of the sides of the peripheral insulation trench 107.

In the example shown, the pixel 100 further comprises transfer grids 121, for example planar transfer grids, located on and in contact with the upper face 101T of the substrate 101. Each transfer grid 121 is for example located at the plumb line of a part of the substrate 101 between region 117 and one of the charge collection zones 119. As a variant, numbers of transfer grids 121 and charge collection zones 119 could be provided different from those shown, for example four charge collection zones 119 associated respectively with four transfer grids 121.

In this example, the photosensitive zones 103 and 105 are intended to be illuminated from the lower face 101B of the substrate 101. As illustrated in Figures 2 and 3, the pixel 100 can also include color filters 123 located on and in contact with the lower face 101B of the substrate 101. In the example shown, each color filter 123 is located directly above one of the first photosensitive zones 103. Each color filter 123 is for example transparent to only part of the visible spectrum, for example for example blue light, and at least part of the infrared spectrum, for example near infrared radiation. Although this has not been shown in Figures 1 to 3, the pixel 100 may also comprise one or more passivation layers, for example interposed between the lower face 101B of the substrate 101 and the color filters 123, and others optical elements such as one or more microlenses.

Although this has not been illustrated, at least one conductive pad can be located on and in contact with the electrically conductive region of the peripheral insulation trench 107. This conductive pad makes it possible to polarize the electrically conductive region of the trench 107. As an example, the electrically conductive region of the peripheral insulation trench 107 is brought to a fixed potential, for example a negative potential, for example equal to about -2 V. This tends to cause an accumulation of holes the along the side walls of the peripheral insulation trench 107. This accumulation of holes makes it possible in particular to prevent photogenerated holes in the photosensitive zone 105 from being trapped at the interface between the substrate 101 and the peripheral insulation trench 107 and also makes it possible to provide a potential adapted to the operation of the photodiode of each of the 2D image pixels.

Furthermore, although this has not been shown in Figures 1 to 3, it is possible to provide another conductive pad located on and in contact with the upper face 101T of the substrate 101, for example near one of the zones of charge collection 119, and a heavily doped region of the second type of conductivity (p+ region, in this example) extending under the upper face 101T of the substrate 101 directly above the conductive pad. The heavily doped region of the second type of conductivity is for example subjected, by the conductive pad, to a substantially zero potential. This makes it possible to provide the holes accumulating along the side walls of the peripheral insulation trench 107.

The pixel 100 may further comprise at least one other conductive pad located on and in contact with the electrically conductive region of each insulation trench 111. These conductive pads are for example intended to polarize the electrically conductive regions of the trenches 111.

During an exposure phase of the pixel 100, electron-hole pairs are for example created inside each photosensitive zone 103. During this phase, the electrically conductive region of each insulation trench 111 is for example carried at a fixed potential, for example a negative potential, for example equal to approximately -1.5 V, by a control circuit (not shown). During the sensor exposure phase, the application of this potential to the electrically conductive region of each trench 111 makes it possible to form a potential barrier in a transfer region located inside each vertical transfer grid TG, between the photosensitive zone 103 and the collection zone 113. In the example shown, the transfer region is bordered by the internal side walls of the peripheral insulation trench 107 and the insulation trench 111, and extends vertically , in the thickness of the substrate 101, under the collection zone 113.

The presence of the potential barrier in the transfer region makes it possible, during the exposure phase, to block a transfer of photogenerated electrons from the photosensitive zone 103 to the collection zone 113. This potential barrier results from the presence, along the side walls of the insulation trenches 107 and 111, of an inversion layer attracting the holes, in this example.

During a reading phase subsequent to the exposure phase, the electrically conductive region of each insulation trench 111 is for example brought to a potential greater than the potential applied during the exposure phase, for example a positive potential, for example equal to approximately 0.5 V, by the control circuit (not shown). The application of this potential to the electrically conductive region of each trench 111 makes it possible to lower, or even eliminate, the potential barrier in the transfer region between the photosensitive zones 103 and the charge collection zones 113. The disappearance of the potential barrier allows, during the reading phase, a transfer 125 of photogenerated electrons from the photosensitive zones 103 to the collection zones 113. For example, the charge collection zones 113 are each brought to a potential fixed, for example a positive potential, for example equal to approximately 2.5 V, during the exposure and reading phases. This makes it possible to attract the photogenerated electrons towards zones 113 during the reading phase.

Furthermore, during an exposure phase of the pixel 100, electron-hole pairs are for example created inside the photosensitive zone 105. During this phase, the electrons photogenerated in the zone 105 are for example transferred, in turn, to the different charge collection zones 119 of pixel 100. For this, one of the planar transfer grids 121 is for example brought to a first potential making it possible to transfer the photogenerated electrons from zone 105 to one of the zones 119, while the other grids 121 are brought to a second potential making it possible to block the transfer of electrons to the other zones 119. Then, another grid 121 is brought to the first potential, the other grids then being brought to the second potential, and so on until all the grids 121 have been successively brought to the first potential. During the same exposure phase, the grids 121 of the pixel 100 are thus sequentially opened, for example by applying to these grids control signals out of phase with each other, in order to allow the transfer of the photogenerated electrons from the photosensitive zone 105 towards a single collection zone 119 at a time. This sequence of opening the transfer gates 121 is for example repeated numerous times during the exposure phase. This allows for example the pixel 100 to implement distance measurements by time of flight, for example indirect Time of Flight measurements ("indirect Time of Flight" - iToF, in English). For example, the opening frequency of each transfer gate 121 is between 10 and 300 MHz and each exposure phase includes a number of opening periods of the transfer gates 121 of between ten thousand and one million. .

During the exposure phase, the grids 121 which are brought to the second potential impose a potential barrier in a transfer region located between the region 117 of the photosensitive zone 105 and the collection zones 119 associated with these grids. This potential barrier results from the presence, under the planar transfer grids 121 brought to the second potential, of an inversion layer attracting the holes, in this example. Conversely, the grid 121 which is brought to the first potential lowers, or even eliminates, the potential barrier in the transfer region located between the region 117 and the charge collection zone 119 associated with this grid. For example, the first potential is positive, for example equal to approximately 0.5 V, and the second potential is lower than the first potential, for example negative, for example equal to approximately -2 V.

For example, the charge collection zones 119 are each brought to a fixed starting potential, for example a positive potential, for example equal to approximately 2.5 V, prior to the exposure phase. This makes it possible to attract the photogenerated electrons towards the zones 119 during the exposure phase. During the exposure phase, the potential of each zone 119 decreases as a function of a number of electrons transferred from the photosensitive zone 105 to this zone 119. At the end of the exposure phase, the potential of the zones 119 is for example measured to determine the total quantity of charges having been integrated by each zone 119 during the exposure phase. Once the measurement is completed, the charge collection zones are for example brought back to the starting potential before the next exposure phase.

In the example shown where the pixel 100 comprises three planar transfer grids 121 respectively associated with three charge collection zones 119, one of the planar transfer grids 121 and the charge collection zone 119 associated with this grid can play a role. a role as an anti-glare device (“antiblooming”, in English). More precisely, one of the planar transfer gates can be controlled so as to allow excess photogenerated charges to be evacuated when the pixel 100 is in the reading phase.

An advantage of the pixel 100 described above in relation to Figures 1 to 3 lies in the fact that the first semiconductor photosensitive zones 103 and the second semiconductor photosensitive zone 105 are superimposed without an intermediate layer, the second photosensitive zone 105 being on and in contact of the first photosensitive areas. This makes it possible in particular to limit losses during the transmission of light from the first photosensitive zones 103 to the second photosensitive zone 105, for example with respect to a pixel in which the photosensitive zones 103 and 105 would each previously be produced on different substrates. , these substrates being subsequently transferred onto each other. In particular, the absence of interconnection structures located between the first photosensitive zones and the second photosensitive zone and formed for example in metallization levels separated from each other by insulating layers makes it possible to limit transmission losses.

There is a schematic and partial top view of an image sensor pixel 200 according to another embodiment. There is a sectional view, according to plan AA of the , from pixel 200 of the .

The pixel 200 of Figures 4 and 5 includes elements in common with the pixel 100 of Figures 1 to 3. These common elements will not be detailed again below. The pixel 200 of Figures 4 and 5 differs from the pixel 100 of Figures 1 to 3 in that the pixel 200 further comprises insulation trenches 201, for example capacitive insulation trenches, surrounding the insulation trenches 111.

In this example, the pixel 100 comprises more precisely four insulation trenches 201 each having, in top view, a general L shape. As illustrated in , each insulation trench 201 extends vertically in the thickness of the semiconductor substrate 101 from the upper face 101T of the substrate 101 to a depth substantially equal to the thickness of the second photosensitive zone 105. In this example, the insulation trenches 201 do not penetrate inside the first photosensitive zones 103. For example, each insulation trench 201 has a depth of between 3 and 18 µm.

In this example, the insulation trenches 201 are, in top view, located at the four corners of the square formed by the peripheral insulation trench 107. The insulation trenches 201 are more precisely arranged so as to delimit regions of the substrate 101 having, in top view, a substantially square shape. In the example illustrated in , parts of the substrate 101 are interposed between the ends of the L formed by each insulation trench 201 and the walls of the peripheral insulation trench 107 located opposite.

Each insulation trench 201 has for example a structure similar to that of the peripheral insulation trench 107. More precisely, although this has not been detailed in Figures 4 and 5, each insulation trench 201 comprises for example an electrically conductive region, for example made of polycrystalline silicon, a metal, for example copper, or a metal alloy. The electrically conductive region of each insulation trench 201 is for example made of the same material as the electrically conductive region of the peripheral insulation trench 107. In addition, each trench 201 comprises for example an electrically insulating layer covering the side walls and the underside of the electrically conductive region. The electrically insulating layer electrically insulates the electrically conductive region of the trench 201 relative to the substrate 101. For example, the electrically insulating layer of each trench 201 is made of a dielectric material, for example silicon oxide. The electrically insulating layer of each insulation trench 201 is for example made of the same material as the electrically insulating layer of the peripheral insulation trench 107.

The electrically conductive region of each insulation trench 201 is for example electrically isolated from the electrically conductive region of the peripheral insulation trench 107. This makes it possible, for example, to polarize the electrically conductive region of each insulation trench 201 independently of the electrically conductive region of the peripheral insulation trench 107. Alternatively, the electrically conductive regions of the insulation trenches 201 may be in contact with the electrically conductive region of the peripheral insulation trench 107.

During the exposure and reading phases of the pixel 200, the electrically conductive region of each insulation trench 201 is brought to a fixed potential, for example a negative potential, for example equal to approximately -2 V. This tends to cause an accumulation of holes along the side walls of the insulation trenches 201. This accumulation of holes makes it possible in particular to avoid, during the reading phase of the first photosensitive zones 103, that holes photogenerated in the second photosensitive zone 105 are not trapped at the interface between the substrate 101 and the insulation trenches 111. In the case of the pixel 200, the regions 115 can also be omitted due to the presence of the insulation trenches 201.

An advantage of the pixel 200 described above in relation to Figures 4 and 5 lies in the fact that the insulation trenches 201 make it possible to control the vertical grids TG associated with the first photosensitive zones 103 while preventing photogenerated charges from being trapped at the interface between the substrate 101 and the insulation trenches 111. This advantageously allows the pixel 200 to simultaneously acquire 2D images and depth images.

Figures 6 to 10 are schematic and partial sectional views, illustrating successive stages of an example of a method of manufacturing the pixel 100 according to one embodiment.

There is a sectional view, according to plan AA of the , illustrating a structure obtained at the end of an ion implantation step, on the side of an upper face 601T of a semiconductor substrate 601, and an epitaxy step of a layer 603 covering the upper face 601T of the semiconductor substrate 601.

The semiconductor substrate 601 is for example a wafer or a piece of wafer of which only a part is represented in . For example, the substrate 601 is made of a semiconductor material, for example silicon. The substrate 601 is for example doped with the first type of conductivity, the n type in this example.

In the example shown, more precisely, during the ion implantation step, a box 605 is formed, extending vertically in the thickness of the substrate 601 from its upper face 601T to a depth less than the thickness of the substrate 601. For example, in the case where the semiconductor substrate 601 is made of silicon, the box 605 is produced by implantation of boron ions (B ³⁺ ) so as to obtain p-type doping.

The layer 603 is then formed, by epitaxial growth, on and in contact with the upper face 601T of the semiconductor substrate 601. The layer 603 is doped with the second type of conductivity, the p type in this example. For example, layer 603 is made of the same material as semiconductor substrate 601.

The semiconductor substrate 601 and the layer 603 for example jointly form the semiconductor substrate 100 of the pixel 100 of Figures 1 to 3.

There is a sectional view, according to plan AA of the , illustrating a subsequent step of producing the peripheral insulation trench 107 and the insulation trenches 111. In the example illustrated in , the insulation trenches 111 border the box 605.

There is a sectional view, according to plan BB of the , illustrating a subsequent ion implantation step on the side of the upper face 101T of the substrate 101.

In the example shown, more precisely, during the ion implantation step, a box corresponding to region 117 extending vertically in the thickness of the substrate 101 from its upper face 101T is formed. More precisely, in this example, region 117 extends vertically from face 101T to a depth less than the thickness of layer 603.

There is a sectional view, according to plan AA of the , a subsequent step of producing charge collection zones 113 and 119 (not visible in ).

The charge collection zones 113 and 119 are for example produced by ion implantation localized on the side of the upper face 101T of the substrate 101.

There is a sectional view, according to plan BB of the , of a subsequent step of producing the transfer grids 121.

The grids 121 are for example obtained at the end of a step of deposition of a layer covering the upper face 101T of the substrate 101, followed by steps of photolithography then etching.

Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will become apparent to those skilled in the art. In particular, the person skilled in the art is capable, from the present description, of adapting the embodiments described to pixels each comprising a number of first photosensitive zones different from that shown in Figures 1 to 5. The person skilled in the art is in particular capable of producing pixels each comprising a second photosensitive zone superimposed on a single first photosensitive zone. In this case, the insulation trench 109 can be omitted and a single vertical transfer grid can be provided. The person skilled in the art is also capable of producing pixels each comprising a second photosensitive zone superimposed on two first photosensitive zones, the first two photosensitive zones being for example separated in this case by a single insulation trench.

Furthermore, the embodiments are not limited to the examples of geometries above. In particular, the pixels, the photosensitive zones and the isolation trenches may have geometries different from those indicated in the present description.

Furthermore, although embodiments have been described above in which the pixel comprises three planar grids 121 associated with three charge collection zones 119, the person skilled in the art is capable of providing a number of grids 121 and of zones 119 depending on the application, for example a grid 121 and a zone 119 intended for the acquisition of the depth image, and a grid 121 and a zone 119 intended for anti-glare.

Finally, the practical implementation of the embodiments and variants described is within the reach of those skilled in the art based on the functional indications given above. In particular, the person skilled in the art is capable of adapting the method described in relation to Figures 6 to 10 to produce the pixel 200 of Figures 4 and 5 from the indications above.

Claims (11)

Image sensor comprising a plurality of pixels (100; 200) formed in and on a semiconductor substrate (101), each pixel comprising:
– at least a first photosensitive zone (103) formed in the semiconductor substrate (101) and adapted to capture light in a first wavelength range;
– a second photosensitive zone (105) formed in the semiconductor substrate (101) directly above said at least one first photosensitive zone (103) and adapted to capture light in a second range of wavelengths, different from the first wavelength range;
– at least one charge collection zone (113) arranged on the side (101T) of the substrate (101) opposite said at least one first photosensitive zone (103);
– at least one transfer region extending from said at least one first photosensitive zone (103) to said at least one charge collection zone (113); And
– at least one transfer grid (TG) extending vertically between said at least one transfer region and the second photosensitive zone and laterally bordering said at least one transfer region. Sensor according to claim 1, in which each pixel (100; 200) further comprises a peripheral insulation trench (107) extending vertically in the semiconductor substrate (101), from said side (101T) of the second photosensitive zone (105), and laterally delimiting said at least one first photosensitive zone (103) and the second photosensitive zone (105). Sensor according to claim 1 or 2, in which each transfer gate (TG) comprises a first insulation trench (111) extending into the semiconductor substrate (101) from said side (101T) of the substrate (101) opposite to said at least one first photosensitive zone (103) and partially penetrating into the thickness of said at least one first photosensitive zone (103). Sensor according to claims 2 and 3, in which each charge collection zone (113) extends laterally between the peripheral isolation trench (107) and the or one of the first isolation trenches (111). Sensor according to any one of claims 1 to 4, in which each transfer gate (TG) is surrounded by a second insulation trench (201) extending vertically in the substrate (101) from said side (101T) of the substrate (101) opposite said at least one first photosensitive zone (103). Sensor according to any one of claims 1 to 5, in which each pixel (100; 200) further comprises at least one other transfer gate (121) extending laterally on said side (101T) of the opposite substrate (101). to said at least one first photosensitive zone (103) and at least one other charge collection zone (119). Sensor according to any one of claims 1 to 6, in which each pixel (100; 200) comprises four first photosensitive zones (103). Sensor according to claim 7, in which the first photosensitive zones are isolated from each other by a third isolation trench (109). Sensor according to any one of claims 1 to 8, wherein the second photosensitive zone (105) is on and in contact with the first photosensitive zone (103). Sensor according to any one of claims 1 to 9, further comprising a control circuit configured to apply alternately, to said at least one transfer grid (TG):
– a first potential adapted to block a transfer of charges from said at least one first photosensitive zone (103) to said at least one charge collection zone (113); And
– a second potential, different from the first potential, adapted to allow a transfer of charges from said at least one first photosensitive zone (103) to said at least one charge collection zone (113). Sensor according to any one of claims 1 to 10, in which the first photosensitive areas (103) of the pixels (100; 200) of the sensor are intended to capture a 2D image and in which the second photosensitive areas (105) of the pixels of the sensor are intended to capture a depth image.